feat: render structured Codex session detail messages

[akolotov]

Summary

This PR improves Codex session details by detecting known structured user messages and rendering them in a readable layout instead of showing raw XML-like wrappers.

It currently supports:

• user_shell_command messages with separate command and result sections
• user_action messages with context, action, and results sections

What Changed

• add backend parsing for supported structured Codex user messages and return an additive structured payload alongside the raw message content
• render supported structured messages in the detail panel with labeled sections and code-style blocks
• preserve plain-text fallback for unknown or malformed payloads
• apply per-field truncation after parsing so large result / results blocks are capped without breaking structured parsing

Notes

• scope is limited to Codex session details
• replay, export, previews, and search continue to use the existing raw message content path
• no new dependencies were added

Screenshots

User Shell Command

User Action

[vakovalskii]

LGTM — additive parser with strict validation (returns null on any anomaly), XSS-safe rendering, plain-text fallback preserved. Scope limited to detail view as documented. Clean.

[NovakPAai]

Code Review

Clean, well-structured implementation. The XML-tag based structured message parsing is solid:

• ✅ Regex-based wrapper detection with proper escaping
• ✅ Field descriptors with max_length truncation prevent unbounded output
• ✅ CSS classes follow existing naming convention
• ✅ Graceful fallback to plain text rendering when parsing fails

One minor note: truncateStructuredField treats maxLength === 0 as "no limit" — this is a reasonable convention but worth documenting in a comment, since 0 usually implies "empty" to readers.